Golang x text encoding

This commits remove the mahonia module and replaces it with the standard functions of the Golang Sub-repositories http://godoc.org/golang.org/x/text/transform and http://godoc.org/golang.org/x/net/html/charset (which are using http://godoc.org/golang.org/x/text/encoding)

This is just one suggestion, I am happy to implement things differently if we want to keep the mahonia module in some form.
I use here 'c' and 'd' in order not to go over 80 chars.